Illuminative light communication device

ABSTRACT

The illuminating end communication device is equipped with an illuminating light source. An electric power fed to the light source is modulated with a modulating unit responding to transmission data, and the modulated light is sent out as illuminating light. The illumination light is received by the light receiving unit of a terminal end communication device to maintain a downlink. Light emitted from the light emitting unit of the terminal end communication device is received by the light receiving unit of the illuminating end communication device to keep an uplink. Or, illuminating light is modulated on the basis of data when it is reflected, whereby data can be transmitted to the illuminating end communication device. It is preferable that illuminating light is reflected by CCR. A high-quality communication is realized using illuminating light of high power.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S patent application Ser. No. 10/532,250 filed Oct. 23, 2003, as International Application No. PCT/JP03/013539, now pending, the contents of which, including specification, claims and drawings, are incorporated herein by reference in their entirety. This application claims priority from Japanese Patent Application Serial No. 2003-004560 filed Jan. 10, 2003, the contents of which are incorporated herein by reference in their entireties.

TECHNICAL FIELD

The present invention relates to a technology that contributes to illuminative light communication.

BACKGROUND ART

In recent years, a radio wave communication system has become available along with portable terminals. Recently, shorter wavelength infrared rays have been widely used due to available frequency depletion. Other than available frequency depletion, radio waves may influence medical devices or various precision equipment. Moreover, there is fear that infrared rays may adversely influence the human body (e.g., eyes). As a result, optical communication is in the spotlight as a safe communication method.

Meanwhile, white LEDs are developed owing to the success of development of blue LEDs. The features of white LEDs are: extremely lower power consumption than that of conventional incandescent lamps or fluorescent lamps, small size, and long life. Accordingly, use of white LEDs as a illuminative light source is considered. Another feature of white LEDs is a fast response speed relative to supplied power. Paying attention to these features, a study of electrically controlling blinking or light intensity and thereby transferring a signal has been conducted.

A study of integration of such signal transfer using white LED lights with the aforementioned power-line communication system has been conducted. For example, a proposal regarding that study has been disclosed in ‘INTEGRATED SYSTEM OF WHITE LED VISIBLE-LIGHT COMMUNICATION AND POWER-LINE COMMUNICATION’ written by inventors: T. Komine, Y. Tanaka, and M. Nakagawa, Institute of Electronics, Information, and Communication Engineers Technical Research Report, The Institute of Electronics, Information, and Communication Engineers, Mar. 12, 2002, Vol. 101, No. 726, pp. 99-104. Since such system utilizes lights, there are no effects on the human body, allowing safe communication. In addition, other applications are expected.

DISCLOSURE OF THE INVENTION

The present invention aims to provide an illuminative light communication device that establishes a downlink using illuminative light, and also allows uplink optical (including infrared rays) communication, or provides, bidirectional optical communication.

According to such objective, an illuminative light communication device, which is positioned on the transmission side for a downlink and positioned on the reception side for an uplink, includes a lighting unit that emits light for lighting a modulator that controls blinking or light intensity of the lighting unit in accordance with data, thereby modulating the emitted light, and a light receiving unit that receives modulated light transmitted from the outside. Data is transmitted via the light emitted by the lighting unit, and the data is received by the light receiving unit. This structure allows establishment of a downlink using illuminative light and an optical uplink by the light receiving unit, thereby allowing bidirectional optical communication.

Note that the lighting unit can be made up of one or multiple LEDs, allowing establishment of a downlink using illuminative light based on the characteristics of the LEDs. In addition, the light receiving unit can receive infrared light or visible light as the modulated light. Furthermore, the light receiving unit may be a two-dimensional sensor. This allows effective removal of noise such as scattered light using received modulated light signals and the other signals. In addition, modulated light can be separated and received from multiple positions using an optical system such as a lens, and uplink data can be received from multiple light emitting sources.

An illuminative light communication device, which is positioned on the transmission side for a downlink and positioned on the reception side for an uplink, includes a light receiving unit that receives illuminative light modulated in accordance with data, thereby capturing the data, and a light emitting unit that emits light modulated in accordance with data to be transmitted. With such structure, the light receiving unit receives downlink illuminative light while the light emitting unit establishes an optical uplink. This allows bidirectional optical communication. A mobile terminal, for example, can carry out bidirectional communication.

Light emitted by the light emitting unit may be infrared light or visible light. In addition, the light emitting unit includes a tracking unit that guides the emitted light to an external light receiving unit, thereby allowing further reliable uplink communication.

An illuminative light communication device, which is positioned on the transmission side for a downlink and positioned on the reception side for an uplink, includes a light receiving unit that receives illuminative light modulated in accordance with data, thereby capturing the data, and a reflecting and modulating unit that reflects the illuminative light and transmits reflected light modulated in accordance with data to be transmitted. Even this structure can provide bidirectional optical communication, where a downlink can be established using illuminative light while an uplink can be established using illuminative reflected light. Furthermore, as described above, illuminative light has very large electric power, and when it is used for an uplink, further reliable communication is possible. In addition, since a new light emitting unit is unnecessary, power consumption can be suppressed to a degree of electric power provided for modulation, which considerably contributes to power saving.

The reflecting and modulating unit may include one or multiple corner cube reflectors (hereafter, referred to as CCR). The CCR is characterized in that incident light is reflected in the same incident direction, and transmits reflected light to a light source of the illuminative light used for a downlink. The reflected light is used for establishing an uplink. With such structure, a tracking unit for guiding light used for an uplink to a light receiving unit is unnecessary. In addition, since incident light from multiple light sources can be reflected in the same direction, respectively, when downlink data is received using illuminative light from multiple light sources, reflected light for an uplink can be transmitted to the respective light sources, thereby allowing reduction in communication error, and improvement in communication quality.

Note that an optical shutter can be used to carry out modulation through controlling reflected light to pass through or be shut off. Alternatively, modulation can be carried out through deforming a reflecting surface of the CCR to change the reflection characteristics of the CCR.

The reflecting and modulating unit may be made up of a corner cube modulation array is made up of multiple CCRs, a lens that is deployed to form an image on the corner cube modulation array, and a modulator that controls every one or every group of the CCRs in the corner cube modulation array to modulate reflected light. As described above, the CCR is characterized in that incident light is reflected in the same incident direction, the CCR on which an image is formed by a light source of illuminative light transmits reflected light to that light source. If there is multiple light sources, the CCRs on which images are formed by the respective light sources transmit reflected light to the corresponding light sources. Therefore, parallel transmission is possible through modulating reflected light for every one or every group of the CCRs corresponding to the respective light sources.

Note that a structure such that an optical shutter is used as a modulator that controls every one or every group of the CCRs to modulate reflected light, or a structure such that the modulator modulates through deforming a reflecting surface of the CCR is possible.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a first embodiment according to the present invention;

FIG. 2 is a diagram describing a modified example of a light receiving unit 213 in a lighting side communication device 201;

FIG. 3 is a diagram describing a modified example of a light emitting unit 222 in a terminal side communication device 202;

FIG. 4 is a schematic block diagram of a second embodiment according to the present invention;

FIG. 5 is a diagram describing an exemplary structure using a mirror as a reflector/modulator 224;

FIG. 6 is a diagram describing a general view of a corner cube reflector (CCR);

FIGS. 7A-7C each is a diagram describing an exemplary modulation method using the CCR; FIG. 7A is a diagram of a structure using an optical shutter; FIG. 7B is a diagram of a structure using a dielectric; and FIG. 7C is a diagram of a structure using an actuator;

FIGS. 8A and 8B each is a graph describing exemplary waveforms of an incident light to the reflector/modulator 224 and a modulated, reflected light; FIG. 8A shows a case where a downlink data transfer rate is faster than an uplink data transfer rate; and FIG. 8B shows a case where the downlink data transfer rate is roughly equal to or less than the uplink data transfer rate;

FIG. 9 is a diagram describing an exemplary usage of an illuminative communication device in which a CCR is provided as the reflector/modulator 224;

FIG. 10 is a diagram describing an exemplary method of combining received signals when multiple lighting side communication devices are provided in the exemplary usage of an illuminative light communication device in which a CCR is provided as the reflector/modulator 224; and

FIG. 11 is a diagram describing an exemplary structure of the reflector/modulator 224 in the terminal side communication device 2 capable of carrying out parallel transmission.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a schematic block diagram of a first embodiment according to the present invention. In the drawing, 201 denotes a lighting side communication device, 202 denotes a terminal side communication device, 211 denotes a modulator, 212 denotes illuminative light sources, 213 denotes a light receiving unit, 214 denotes a filter, 221 denotes a light receiving unit, 222 denotes a light emitting unit, and 223 denotes a processor. The lighting side communication device 201 is used as a lighting element to illuminate the vicinity thereof, and includes the illuminative light sources 212, which emit light for lighting. In this exemplary structure, a light source is LEDs, but is not limited to them. Alternatively, LDs or other light emitting devices with a fast response speed are available.

The lighting side communication device 201 also includes the modulator 211 and the light receiving unit 213 for illuminative light communication. The modulator 211 ,which is deployed for a downlink, controls electric power, which is supplied to the illuminative light sources 212, in accordance with data to be transmitted. This allows control of light intensity or blinking of the illuminative light sources 212 and emission of light modulated in accordance with data. The terminal side communication device 202 to be described later then receives the modulated illuminative light, thereby allowing data transmission from the lighting side communication device 201 to the terminal side communication device 202 (downlink).

An arbitrary modulation system, such as on-off keying (OOK) or binary phase shift keying (BPSK), is available. In addition, all of or some of the illuminative light sources 212 for lighting may be LEDs, which are controlled to change light intensity or blinking. Note that since LEDs have a high-speed response characteristic as described above, change in light intensity and/or blinking is imperceptible to the human eye, and seems as if light is emitted continuously. Accordingly, the illuminative light sources 212 may be used for lighting besides data communication.

The light receiving unit 213, which is provided for receiving modulated light (such as infrared rays, visible light, ultraviolet light) emitted from the terminal side communication device 202, includes a light receiving device such as a photodiode. In addition, in this exemplary structure, a filter 214 is provided for selectively receiving modulated light emitted from the terminal side communication device 202. For example, to receive infrared rays, the filter 214 that allows infrared rays to pass through should be provided. Needless to say, a structure without the filter 214 is possible. In this case, received light is converted into an electric signal, which is then demodulated. Consequently, data from the terminal side communication device 202 is reconstructed and then output.

Note that data to be transmitted via illuminative light may be data received from the outside, or data retained in or generated by the lighting side communication device 201. Alternatively, data received by the light receiving unit 213 may be output to the outside or processed in the lighting side communication device 201.

The terminal side communication device 202 may be an arbitrary terminal device, and may include the light receiving unit 221 and the light emitting unit 222 for illuminative light communication and the processor 223 for various kinds of processing. The light receiving unit 221 receives and demodulates modulated light emitted from the lighting side communication device 201, and transmits the demodulated results to the processor 223. In this manner, reception of data transmitted from the lighting side communication device 201 via illuminative light is possible, or establishment of a downlink is possible.

The light emitting unit 222, which includes a light source such as LEDs or LDs, and a control circuit for turning on and off the light sources, receives data to be transmitted from the processor 223, controls light intensity or blinking of the light sources in accordance with data, and emits the resulting modulated light. At this time, any modulation system can be used for that modulation. Alternatively, infrared rays, visible light, or ultraviolet light may be used as light to be emitted. The light receiving unit 213 of the lighting side communication device 201 described above then receives the modulated light, or an uplink is established.

As described above, the lighting side communication device 201 has the illuminative light sources 212 illuminate the vicinity thereof, and modulates the illuminative light in accordance with data, allowing transmitting the data via the illuminative light. The light receiving unit 221 in the terminal side communication device 202 then receives this illuminative light, thereby receiving data transmitted from the lighting side communication device 201. In this manner, a downlink is established. In addition, the terminal side communication device 202 has the light emitting unit 222 emit modulated light in accordance with data, thereby transmitting data. The light receiving unit 213 of the lighting side communication device 201 then receives this modulated light, and thus the lighting side communication device 201 receives data transmitted from the terminal side communication device 202. In this manner, an uplink is established. In this manner, either downlink or uplink optical communication is possible, or bidirectional optical communication is possible.

For example, the terminal side communication device 202 may be a mobile, portable terminal device, such as a notebook computer, a PDA, or a cellular phone, which does not need cable connection. More specifically, in the case of a PDA with a camera or a cellular phone with a camera, the camera may be used as the light receiving unit 221. In addition, the terminal side communication device 202 is available in an environment where radio wave communication is restricted, such as a hospital, a train, an airplane, a spaceship, or a site where pacemaker users exist, and no license for use thereof is required. Needless to say, it is available in various environments, such as ordinary offices, stores, homes, and public facilities. In addition, not limited to indoors, it is available for various applications, such as neon signs, lighting for advertisement, and communication among automobiles or among facilities on the street and automobiles in a transportation system.

Moreover, optical wavelength is short, allowing very higher-speed communication than radio wave communication. Furthermore, typically, lighting elements are widely provided, and lighting is naturally provided in an environment where terminal devices are used. Such lighting elements may be used as the lighting side communication device 201 for communication, resulting in considerable reduction in installation cost.

Note that in an environment such as an office where multiple lighting elements are provided, respective lighting elements may be used as the lighting side communication device 201, and multiple lighting side communication devices 201 can be deployed. In this case, light emitted from a single terminal side communication device 202 can be received by the multiple lighting side communication devices 201. In this manner, light is received by the multiple lighting side communication devices 201, allowing improvement in communication quality. In addition, even when a single lighting side communication device 201 cannot receive light due to shadowing developed by a passerby, other lighting side communication devices 201 can receive that light, solving such problem of shadowing.

Next, several major modified examples of the first embodiment are described. FIG. 2 is a diagram describing a modified example of the light receiving unit 213 in the lighting side communication device 201. In the drawing, 231 denotes a two-dimensional sensor, and 232 denotes a lens. The two-dimensional sensor 231 is used as the light receiving unit 213 in the lighting side communication device 201, and the lens 232 is used to form an image on the light receiving surface. With such structure, an image due to light emitted from the terminal side communication device 202 is formed on the light receiving surface of the two-dimensional sensor 231, and that light is received by some of a great number of light receiving cells provided in the two-dimensional sensor 231. At this time, since the other light receiving cells receive environmental light, background noise can be removed using it, allowing high-quality communication.

In addition, when there are multiple terminal side communication devices 202 and 202′, for example, in the light receiving area, an image due to lights emitted from the respective terminal side communication devices 202 and 202′ are formed at different positions of the two-dimensional sensor 231, as shown in FIG. 2. This allows parallel reception of data from the respective terminal side communication device 202 and 202′. Needless to say, a case of three or more terminal side communication devices provided provides the same advantage.

In addition, in an environment where multiple lighting side communication devices 201 are provided, light emitted form the respective terminal side communication devices 202 and 202′ can be received by the two-dimensional sensors 231, which are provided in the respective lighting side communication devices 201. In this case, communication quality can be improved by identifying light received points in the respective two-dimensional sensors 231 from the light received positions in the respective two-dimensional sensors 231 and the position of the lighting side communication device 201.

FIG. 3 is a diagram describing a modified example of the light emitting unit 222 in the terminal side communication device 202. In the drawing, 241 denotes a tracking unit, 242 denotes LED light sources, 243 denotes a mirror surface, and 244 denotes a lens. According to the basic structure shown in FIG. 1, when the LED light sources 242 are used as the light source of the light emitting unit 222 in the terminal side communication device 202 emitted light diverges, resulting in decrease in intensity of light received by the lighting side communication device 201. FIG. 3 shows an exemplary structure having the mirror surface 243 and the lens 244 provided to prevent such divergence of emitted light and narrow a light beam. Light emitted from the LED light sources 242 may be effectively provided to the lighting side communication device 201 using such an optical system, allowing preferable communication. Needless to say, when LDs with high directivity are used as the light source, the mirror surface 243 and the lens 244 are unnecessary.

In addition, in the case of narrowing the light beam or using LDs as a light source, communication quality decreases or communication is impossible when emitted light does not correctly hit the light receiving unit 213 in the lighting side communication device 201. Therefore, in the exemplary structure shown in FIG. 3, the tracking unit 241 is provided to guide the light beam to the light receiving unit 213 in the lighting side communication device 201. The tracking unit 241 may be structured with a movable mechanism that allows manual change in light beam direction. Alternatively, it may be structured to automatically operate according to illuminative light or operate under control of a terminal device itself. Alternatively, it may be structured to be controlled by the lighting side communication device 201 via a downlink. In this manner, there are a variety of structures to embody the tracking unit 241.

A modified example of the light receiving unit 213 in the lighting side communication device 201 and a modified example of the light emitting unit 222 in the terminal side communication device 202 have been described above. The present invention is not limited to those examples. For example, the structure shown in FIG. 2 may be applicable to the light receiving unit 221 in the terminal side communication device 202. This allows parallel illuminative light transmission of different pieces of data from multiple lighting side communication devices and selective reception of those pieces of data by the terminal side communication device 202.

In addition, data to be transmitted from the lighting side communication device 201 and data received therefrom may be transferred via a dedicated data line or may be superimposed on an electric power waveform and transmitted via a power line, which supplies electric power for lighting. Needless to say, besides the above-mentioned systems, various modifications thereof are possible.

FIG. 4 is a schematic block diagram of a second embodiment according to of the present invention. In the drawing, the same symbols are given to the same parts as those in FIG. 1, and repetitive descriptions thereof are thus omitted. 224 denotes a reflector/modulator. In the aforementioned first embodiment, an exemplary structure such that the light emitting unit 222 is provided in the terminal side communication device 202 to emit light for establishment of an uplink is shown. On the other hand, the second embodiment shows a structure such that illuminative light for a downlink is used as is, and reflected light is used for an uplink. As described above, illuminative light has large electric power, and when it is used for an uplink, further reliable communication is possible. In addition, since the light emitting unit 222 is unnecessary in the terminal side communication device 202, power consumption of the terminal side communication device 202 can be considerably suppressed, greatly contributing to power saving. Note that since the structure of the lighting side communication device 201 can be the same as those of the aforementioned first embodiment and the modified example thereof, repetitive descriptions thereof are thus omitted, and the modulator 211 is not shown in the drawing. In addition, the light receiving unit 221 in the terminal side communication device 202 may be the same as those of the aforementioned first embodiment and the modified example thereof.

The reflector/modulator 224 is provided in the terminal side communication device 202, which allows use of illuminative light for an uplink. The reflector/modulator 224 reflects illuminative light and transmits the resulting reflected light, which is modulated in conformity with to-be-transmitted data via an uplink.

FIG. 5 is a diagram describing an exemplary structure with a mirror used as the reflector/modulator 224. In the drawing, 251 denotes a mirror, 252 denotes an optical shutter, 253 denote a shielding wall, and 254 denotes a tracking unit. The mirror 251 is simply used for reflecting illuminative light, and the reflection direction is controlled by the tracking unit 254, which is similar to the tracking unit 241 of the modified example shown in FIG. 3. In addition, modulation can be carried out using the optical shutter 252 allowing incident light to the mirror 251 and reflected light from the mirror 251 to pass through or be shut off. For example, a liquid crystal shutter may be used as the optical shutter 252 for modulation, which controls the orientation of liquid crystal in accordance with data so as to allow reflected light to pass through or be shut off. Needless to say, other modulation methods may be used alternatively. For example, reflection direction of the mirror surface may be changed in accordance with data. In other words, since change in reflection direction of the mirror surface changes the intensity of incident light to the light receiving unit 213 in the lighting side communication device 201, data can be captured by detecting this change. In this case, the tracking unit 254 may also be used as a modulation means.

In addition, in the exemplary structure shown in FIG. 5, the shielding wall 253 is provided surrounding the mirror 251. This is provided for protecting user's eyes from the brightness of reflected light traveling from the mirror 251, which reflects light emitted by a light source other than the light source in the lighting side communication device 201 for communication. When the illuminative light source 212 and the light receiving unit 213 of the lighting side communication device 201 are provided closely, only light from the illuminative light source 212 should be reflected, returning to the light receiving unit 213, and thus reflection of other lights is unnecessary. The shielding wall 253 is provided for preventing such unnecessary reflection. Alternatively, the inner surface of the shielding wall 253 may be formed to be a mirror, thereby increasing reflected light intensity. Needless to say, a structure without the shielding wall 253 is possible.

Note that the unit shown in FIG. 5 may be used as a single structure or multiple units may be provided.

A corner cube reflector (CCR) may be used as an illuminative light reflecting means in the reflector/modulator 224. FIG. 6 is a diagram describing a general view of the CCR. The CCR has three reflecting surfaces orthogonal to each other in an inward direction. For example, as shown in FIG. 6, it can be structured with three inner reflecting surfaces of a cube or a rectangular, which have a shared apex and are orthogonal to one another.

The CCR is characterized in that incident light is reflected in the same incident direction. Accordingly, when illuminative light hits, the illuminative light is then reflected toward the light source of the illuminative light. According to the present invention, illuminative light is used for a downlink, and the illuminative light used for the downlink is reflected and also used for an uplink. More specifically, since the illuminative light is reflected toward the illuminative light source, the reflected light can be received by the light receiving unit 213 arranged very close to the illuminative light source in the lighting side communication device 201. In addition, since high directivity/strongly reflected light hits the light receiving unit 213 in the lighting side communication device 201, there is an advantage that peripheral light is difficult to adversely influence that light. Note that the lighting side communication device 201 can be provided in an arbitrary area, and even when the terminal side communication device 202 is provided in an arbitrary area, reflected light is reflected toward the lighting side communication device 201.

FIGS. 7A-7C each is a diagram describing an exemplary modulation method using the CCR. In the drawing, 261 denotes the CCR, 262 denotes an optical shutter, 263 denotes a dielectric, and 264 denotes an actuator. Illuminative light can be reflected by the CCR toward the lighting side communication device 201 in the aforementioned manner. Several methods of modulating this reflected light in accordance with data are shown forthwith. FIG. 7A shows an example of modulating with the optical shutter 262 arranged in front of the CCR. The optical shutter 262 may be structured with a liquid crystal shutter using a liquid crystal display. The liquid crystal orientation of the liquid crystal shutter changes due to application of a voltage, thereby switching over between a light pass-through mode and a light shut-off mode. When this liquid crystal shutter is controlled to allow light to pass through, illuminative light from the lighting side communication device 201 hits the CCR 261, and the resulting reflected light then travels to the lighting side communication device 201, as described above. On the other hand, when the liquid crystal shutter is controlled to shut off light, both incident light to the CCR 251 and reflected light are shut off, and the light receiving unit 213 in the lighting side communication device 201 cannot receive reflected light. In this manner, the control of liquid crystal orientation of the liquid crystal shutter allows reflected light to pass through or be shut off. Reflected light modulated through such a shutter operation in accordance with data may be transmitted to the lighting side communication device 201. Needless to say, there are various kinds of liquid crystal, and they are available as needed. For example, a type of liquid crystal capable of changing over between a light pass-through mode and a light reflecting mode is available. In addition, in this exemplary structure, a liquid crystal shutter is used as the optical shutter 262. Alternatively, any type of shutter mechanism capable of being controlled to allow illuminative light and reflected light entered to pass through to the CCR 261 or prevent them from passing through is available regardless of its structure.

In the example shown in FIG. 7B, the dielectric 263 is deployed very close (λ/3) to part of or entirety of the mirror surface, which constitutes the CCR 261, so as to decrease the total amount of reflection from the inner surfaces. The intensity of reflected light from the CCR 261 may be controlled by changing the position of the dielectric in accordance with data, allowing transmission of modulated, reflected light to the lighting side communication device 201. Note that this method utilizes coherence, and use thereof is limited to the case where LDs are used as a light source in the lighting side communication device 201.

In the example shown in FIG. 7C, the actuator 264 is attached to one of the mirror surfaces, which constitute the CCR 261, so as to change the mirror surface in accordance with data. For example, by changing an angle or deforming the mirror surface, a light reflected angle between adjacent mirror surfaces of the CCR 261 changes. As a result, the relationship between incident light and reflected light such that the latter returns along the former can be broken. Such control in accordance with data allows transmission of modulated, reflected light to the lighting side communication device 201. The actuator 264 may be a structure using a driving capability of a mechanical micro machine or distortion of a piezo element.

FIG. 8 is a graph describing exemplary waveforms of incident light to the reflector/modulator 224 and modulated reflected light, respectively. As described above, incident light to the reflector/modulator 224 is illuminative light that is modulated and emitted from the lighting side communication device 201. Accordingly, light intensity or blinking is controlled in accordance with data transmitted via a downlink. When the light is reflected by the CCR 261, the reflected light on which data transmitted via the downlink is still being superimposed is then provided. However, when the uplink data transfer rate is slower than the downlink transfer rate, there is no problem. For example, if the uplink data transfer rate is slow, illuminative light intensity changes many times during a single data transfer due to high-speed change in illuminative light intensity as shown in FIG. 8A. For example, when modulation is carried out and incident light is reflected by the CCR 261 as described in FIG. 7, average light intensity between a bright and a dark area during a single data transfer is received by the light receiving unit 213 in the lighting side communication device 201. On the other hand, when the CCR 261 does not reflect light toward the light source, the light receiving unit 213 in the lighting side communication device 201 cannot even receive average light intensity. Therefore, data can be reliably transferred even using illuminative light on which data for a downlink is still being superimposed for an uplink.

On the other hand, when the downlink data transfer rate is roughly equal to or lower than the uplink data transfer rate, reflected illuminative light is available for an uplink if there is no time when illuminative light is completely shut off. FIG. 8B shows a case of the downlink data transfer rate being equal to the uplink data transfer rate. In this example, sub carrier binary phase shift keying (BPSK) is used as a downlink data modulation system. In this case, since illuminative light intensity never continuously stay in zero during single data transfer, the light receiving unit 213 in the lighting side communication device 201 can receive uplink data through sensing change in received light intensity even when modulation is carried out by allowing illuminative light to pass through or be shut off for an uplink.

In this manner, even when illuminative light is modulated, an uplink from the terminal side communication device 202 to the illumination light communication device 201 can be established by reflecting the modulated illuminative light and then modulating it in conformity with uplink data. Illuminative light has large electric power, and reflected light thereof also has large electric power. This allows high-quality uplink communication. In addition, since with a structure of using the CCR 261, reflected light returns to the incident light source, there is no need for tracking, and an uplink can be established with a simple structure. Moreover, there is an advantage that it is unnecessary to synchronize with the downlink. Furthermore, when using the CCR 261, irregular reflected light scarcely hits users' eyes, and thus the users scarcely sense brightness.

FIG. 9 is a diagram describing an exemplary application of the illuminative light communication device which has the CCR as the reflector/modulator 224. FIG. 10 is a diagram describing an exemplary received signal combining method for the multiple lighting side communication devices. In the drawing, 271 denotes light receiving devices, 272 denotes delay correcting units, 273 denotes a combining unit, and 274 denotes a demodulator. As described above, the CCR is characterized in that it returns reflected light toward the light source. This feature is the same as that in the case where incident lights from multiple directions hit. For example, as shown in FIG. 9, when multiple lighting side communication devices 201, 201′, and 201″ emit respective illuminative lights, which then enter the terminal side communication device 202, illuminative light from the lighting side communication device 201 is reflected thereto by the CCR in the terminal side communication device 202, illuminative light from the lighting side communication device 201′ is reflected thereto, and illuminative light from the lighting side communication device 201″ is reflected thereto. As a result, uplink data transmitted from the terminal side communication device 202 is received by the multiple lighting side communication devices 201, 201′, and 201″.

The multiple lighting side communication devices 201,201′, and 201″ can reliably receive data by combining electric signals obtained through reception of light. An exemplary circuit structure in this case is shown in FIG. 10. The light receiving devices 271 in the respective light receiving units 213 of the respective lighting side communication devices 201, 201′, and 201″ convert received lights to electric signals. The electric signals from the light receiving devices 271 are corrected for specified amounts of delays for respective lighting side communication devices 201, 201′, and 201″ by the delay correcting unit 272, and the resulting corrected electric signals are then combined by the combining unit 273. This may be done through simple addition, average electric power calculation, and/or weighting. The higher the signal intensity, the larger weight to be added. The combined electronic signals are demodulated by the demodulator, allowing data transmitted from the terminal side communication device 202 to be captured.

In this manner, since uplink data can be transmitted to the multiple lighting side communication devices, even if shadowing develops due to a passerby, which may cause disturbance of optical transmission to a lighting side communication device, other lighting side communication devices can receive light, allowing reliable communication. In this case, a CCR tracking mechanism is unnecessary, and disturbance of optical communication or shadowing can be solved by a simple structure. Note that three lighting side communication devices are shown in FIG. 9, but the present invention is not limited to this. Alternatively, two or four devices are available.

A case of using a single CCR has been described above; alternatively, multiple CCRs may be provided, for example, two-dimensionally. When multiple CCRs are provided, a modulating structure as shown in FIG. 7 should be provided for each of CCRs 261. By controlling all of them in the same manner, they can operate in the same manner as in the case of using a single CCR. For example, with a structure where the optical shutter 262 is used for modulation as shown in FIG. 7A, the optical shutter 262 may be shared by multiple CCRs.

In the case of providing multiple CCRs, it is possible to control respective multiple CCRs or respective groups of multiple CCRs to modulate. With such a structure, parallel data transmission from the terminal side communication device 202 is possible. FIG. 11 is a diagram describing an exemplary structure which allows parallel transmission of the reflector/modulator 224 in the terminal side communication device 202. In the drawing, 281 denotes a CCR array, and 282 denotes a lens. The CCR array 281, which is made up of multiple CCRs, is structured such that respective multiple CCRs or respective groups of multiple CCRs can be controlled for modulation. When modulation for individual CCRs 281 is required using the optical shutter 262 shown in FIG. 7A, an optical shutter capable of controlling for respective multiple CCRs or respective groups of multiple CCRs should be provided. In addition, with the structure allowing CCR mirror surfaces to change as shown in FIG. 7C, the same structure can be provided for individual CCRs, and control for respective multiple CCRs or respective groups of multiple CCRs is possible.

The lens 282 is provided at the entrance (or exit) of the CCR array 281 and is controlled to form an image for illuminative lights, which have traveled from the lighting side communication devices 201 and 201′ on the CCR mirror surface or in the vicinity thereof. With such a structure, incident lights emitted from the lighting side communication devices 201 and 201′ hit only some of the CCRs in the CCR array 281. According to the characteristics of the CCR, some of the CCRs that incident illuminative light from the lighting side communication device 201 hits return reflected light thereto, while some of the CCRs that incident illuminative light from the lighting side communication device 201′ hits return reflected light thereto. At this time, when the CCRs that respective incident illuminative lights hit are controlled to modulate in the same manner, the same data can be transmitted to the multiple lighting side communication devices 201 and 201′ as described in FIG. 9.

Alternatively, CCRs that respective incident illuminative lights hit may be controlled to modulate in accordance with different pieces of data. In other words, the CCRs that incident illuminative light from the lighting side communication device 201 hits and that return reflected light thereto may be controlled to modulate in accordance with a first data while CCRs that incident illuminative light from the lighting side communication device 201′ hits and that return reflected light thereto may be controlled to modulate in accordance with a second data. This allows transmission of the first data to the lighting side communication device 201 and the second data to the lighting side communication device 201′. Those pieces of data can be transmitted in parallel, allowing parallel communication.

Note that: CCRs that incident illuminative light hits may be predetermined; a simply structured light reception device may be provided together with CCRs; a light reception device may be combined with the CCR mirror surface; and/or a two-dimensional sensor and a lens system may be used as the light receiving unit 221 in the terminal side communication device 202 to allow identification of the position of the lighting side communication device. Needless to say, other structures are available.

The example of using reflected illuminative light for an uplink has been described above as the second embodiment. As with the aforementioned first embodiment, in the second embodiment, the lighting side communication device 201 may be provided in the same manner as conventionally available lighting elements, and the terminal side communication device 202 may be a portable terminal device, such as a notebook computer, a PDA, or a cellular phone. In addition, it is available in ordinary offices, stores, homes, public facilities, and an environment where radio wave communication is restricted such as hospitals, trains, airplanes, spaceships, and a site in which pacemaker users exist. Furthermore, use thereof is not limited to the indoors, and it is available for various applications, such as neon signs, lighting for advertisement, or communication among automobiles or among facilities on the street and automobiles in a transportation system.

Moreover, the second embodiment may be modified into various modifications as with the aforementioned first embodiment. The structure of the light receiving unit 213 in the lighting side communication device 201 shown in FIG. 2 and structure of the light emitting unit 222 in the terminal side communication device 202 shown in FIG. 3 may be used, and power line communication for data transmitted from and received by the lighting side communication device 201 is available. Needless to say, besides such modifications, a variety of other modifications are possible.

As described above, the conventional illuminative light communication allows only downlink optical communication. However, the present invention allows uplink optical communication, allowing bi-directional optical communication.

In addition, reflected illuminative light may be used for an uplink. In this case, high-quality communication is possible using illuminative light with large electric power. Furthermore, use of CCRs allows establishment of uplink optical communication with a simple structure that does not need tracking. 

1. An illuminative light communication device, comprising: a lighting unit that emits light for lighting; a modulator that controls blinking or light intensity of the lighting unit in accordance with data, thereby modulating the emitted light; and a light receiving unit that receives modulated light transmitted from the outside; wherein data is transmitted via the light emitted by the lighting unit, and the data is received by the light receiving unit.
 2. The illuminative light communication device according to claim 1, wherein the lighting unit is made up of one or a plurality of LEDs.
 3. The illuminative light communication device according to claim 1, wherein the light receiving unit receives infrared light as the modulated light.
 4. The illuminative light communication device according to claim 1, wherein the light receiving unit receives visible light as the modulated light.
 5. The illuminative light communication device according to claim 1, wherein the light receiving unit is a two-dimensional sensor.
 6. An illuminative light communication device, comprising: a light receiving unit that receives illuminative light modulated in accordance with data, thereby capturing the data; and a light emitting unit that emits light modulated in accordance with data to be transmitted.
 7. The illuminative light communication device according to claim 1, wherein the light emitting unit emits infrared light.
 8. The illuminative light communication device according to claim 1, wherein the light emitting unit emits visible light.
 9. The illuminative light communication device according to claim 6, wherein the light emitting unit comprises a tracking unit that guides the emitted light to an external light receiving unit.
 10. An illuminative light communication device, comprising: a light receiving unit that receives illuminative light modulated in accordance with data, thereby capturing the data; and a reflecting and modulating unit that reflects the illuminative light and transmits reflected light modulated in accordance with data to be transmitted.
 11. The illuminative light communication device according to claim 10, wherein the reflecting and modulating unit is structured including one or a plurality of corner cube reflectors, and transmits reflected light to a light source of the illuminative light.
 12. The illuminative light communication device according to claim 10, wherein the reflecting and modulating unit uses an optical shutter to carry out modulation.
 13. The illuminative light communication device according to claim 11, wherein the reflecting and modulating unit modulates through deforming a reflecting surface of the corner cube reflector.
 14. The illuminative light communication device according to claim 10, wherein the reflecting and modulating unit comprises: a corner cube modulation array comprising a plurality of corner cube reflectors; a lens that is deployed to form an image on the corner cube modulation array; and a modulator that controls every one or every group of the corner cube reflectors in the corner cube modulation array to modulate reflected light.
 15. The illuminative light communication device according to claim 14, wherein the modulator is an optical shutter.
 16. The illuminative light communication device according to claim 14, wherein the modulator modulates through deforming a reflecting surface of the corner cube reflector. 